Generally speaking, the field of drug delivery can be described as encompassing approaches, formulations, technologies and systems for transporting a pharmaceutical compound in the body to achieve one or more desired therapeutic effects. Drug delivery techniques may involve systemic administration and/or site-specific delivery of one or more drugs within the body. In order to achieve the desired therapeutic effect(s), systemic and site-specific approaches typically take into account both quantity and duration of drug presence.
Drug delivery may involve release of drug from a surface of a medical article, for example, release of drug from a coating provided on a surface of a medical article. In these aspects, drug delivery techniques can be concerned with modulating the release profile of a drug from such coatings to achieve a desired dosage of the drug. Delivery of hydrophilic drugs can present challenges. Drug elution rates for a coating containing a hydrophilic or lipophilic drug are typically very fast initially when the article contacts body fluid or blood. This is the so-called “burst effect.” Multilayer coatings that include a topcoat over drug containing layers have been used to control release of drugs. However, small defects in coatings, including cracks, abrasions and cuts, or even water absorption by the topcoat, can lead to rapid burst release of hydrophilic drugs. As such, it is difficult to design coatings which stably entrap or encase a water soluble drug and allow controlled release of the water soluble drug over periods of days or weeks.